Disk storage drive having motor drive with non-corrodible hub

ABSTRACT

A disk storage drive is provided with a brushless drive motor having a stator with a winding. An external rotor coaxially surrounds the stator and is spaced therefrom by a substantially cylindrical air gap. The rotor includes a permanent magnet and a soft magnetic yoke. A hub is provided that is concentric to the yoke and is connected to the rotor for rotation therewith. The hub has a disk mounting portion on its outer peripheral surface that can be passed through the central opening of a standardized storage disk for mounting the storage disks for rotation therewith. At least half of the axial longitudinal dimension of the stator winding and the rotor magnet interacting therewith is housed within the disk mounting portion of the hub. The hub is made from a non-ferromagnetic material that is suitable for storage drive clean chamber use after dimensional finishing of the hub.

This application is a continuation, of application Ser. No. 733,231filed May 10, 1985 now abandoned which is a continuation-in-part ofapplication Ser. No. 412,093 filed Aug. 27, 1982 and now abandoned.

.Iadd.This is an application for reissue of U.S. Pat. No. 4,779,165,issued Oct. 18, 1988, entitled "DISK STORAGE DRIVE". .Iaddend.

BACKGROUND OF THE INVENTION

The invention relates to a disk storage drive for receiving at least onestorage tank having a central opening, with an outer rotor type drivingmotor having a rotor casing mounted by means of a shaft in a bearingsystem so as to rotate relative to a stator and on which can be placedthe storage disk for driving by the rotor casing, as described in U.S.patent application Ser. No. 353,584, now U.S. Pat. No. 4,438,542, issuedMar. 27, 1984.

The content of this patent is incorporated herein by reference to avoidunnecessary repetition. It relates to a disk store and storage drive forreceiving at least one storage disk having a central opening. Thedriving motor extends coaxially at least partly through the centralopening of the storage disk, and means are provided for connecting thestorage disk and the driving motor rotor.

BRIEF SUMMARY OF THE INVENTION

The problem of the present invention is to further simplify theconstruction of a disk store described in the aforementioned U.S. Pat.No. 4,438,542, while improving its operation. In particular, the storagedisk is to be reliably protected against undesired influencing by themagnetically active parts of the driving motor. In addition, aparticularly space-saving and robust construction of the driving motorare to be achieved.

According to the invention, this problem is solved in that at least thepart of the rotor casing receiving the storage disk is made from anon-ferromagnetic material and carries the shaft directly or by means ofa hub and in that a magnetic shield made from a ferromagnetic materialin the form of a drawn can projects into the storage disk receiving partof the rotor casing and is connected thereto. The shielding surroundsthe periphery of the magnetically active parts of the driving motor andalso envelops the parts at one end. The shield has a central openingwhose edge is directly radially adjacent the shaft or parts of thedriving motor carrying or supporting the shaft. A rotor casingconstructed in this way can be easily manufactured, and it effectivelyprotects the magnetically sensitive storage disks, particularly magnetichard storage disks, against magnetic stray flux emanating from themagnetically active parts of the driving motor. The shield is preferablyin the form of a deep-drawn can, and the part of the rotor casingreceiving the storage disk can be made from a lightweight metal by diecasting.

If, in the manner described in the aforementioned U.S. Pat. No.4,438,542, the driving motor is constructed as a brushless directcurrent motor with a permanent magnet rotor, then in accordance with afurther development of the invention a printed circuit board with atleast one rotary position detector and perhaps other electroniccomponents for the control and regulation of the driving motor aremounted on the side of the stator remote from the bottom of theshielding can. This ensures that the rotary position detector and anyfurther circuit components of the magnetic shielding arrangement do notinterfere with the rotating parts.

Further advantageous development of the invention also are disclosed,including features that contribute to a compact construction of the diskstorage drive. In connection with disk storage drives of the presenttype, high demands are made on the concentricity of the storage disks.It is therefore generally necessary to machine the storage diskreceiving part or to work it in some other way so that it isdimensionally true. As a result of other features of the invention, thenecessary machining is reduced to a relatively small part of thecircumferential surface of the storage disk receiving part and atrouble-free engagement of a storage disk on the shoulder of the storagedisk receiving part is permitted.

Other features of the claimed invention provide a robust precisionmounting support for utilizing the available axial overall length formaximizing the distance between the bearings; and permit particularlylarge distances between the bearings where the axial installation areabetween a mounting or assembly flange and the end of the storage diskreceiving part is limited. Installation space is available on the otherside of this flange. Still other features provides for alternativesolutions leading to particularly small radial runouts of the rotor;ensure a space-saving housing of the circuit board; and for solutionswhere importance is attached to particularly shallow construction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter relative tonon-limitative embodiments and the attached drawings, wherein:

FIG. 1 is a vertical partial sectional view through a first embodimentof the invention along the line I--I of FIG. 2;

FIG. 2 is a plan view of the arrangement of FIG. 1;

FIG. 3 is a sectional view through another embodiment of the inventionwith an extended bearing tube;

FIG. 4 is a sectional view through a further embodiment of theinvention; *

FIG. 5 is a section through a disk storage drive according to theinvention along line V--V of FIG. 6;

FIG. 6 is a diagrammatic section along line VI--VI of FIG. 5;

FIG. 7 is a section similar to FIG. 6 for a modified embodiment;

FIG. 8 is an axial section through a disk storage drive according to afurther modified embodiment of the invention;

FIG. 9 is an axial partial section for a further modified embodiment;

FIG. 10 is an axial partial section for an embodiment with a magneticyoke ring and separate axial shield ring;

FIG. 11 is an axial partial section through a further modifiedembodiment of a disk storage drive with a fixed shaft; and

FIG. 12 is a partial section corresponding to FIG. 11 for an embodimentwith a fixed shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disk storage drive illustrated in FIG. 1, having an extremelyshallow construction, has a brushless direct current motor 45 having arotor casing 47 fixed to and coaxial with a rotor shaft 46. A statorlamination 48, carrying a stator winding 49 is mounted on a bearing tube50. The rotor shaft 46 is rotatably mounted within the bearing tube 50by means of two bearings 52 and 53. These are kept axially spaced by apair of retaining rings 54. A cup spring 55 is supported on theunderside of the bearing 53 by a retaining ring 56 resting on the rotaryshaft 46, so that the bearing 52, 53 are axially braced relative to oneanother. The bearings 52, 53 are pressed into the bearing tube 50 at thetime of assembly. Together with an assembly flange 24, the bearing tube50 forms a one-piece die casting.

The rotor casing 47 comprises a storage disk receiving part 25 and ashielding can 26, which are joined together, for example, by riveting.The storage disk receiving part 25 is made from a non-ferromagneticmaterial, preferably lightweight metal. The rotor shaft 46 is pressedinto a central opening of the storage disk receiving part 25. Asalternative, the shaft can be cast into the receiving part.

The shielding can 26 is made from a ferromagnetic material and can inparticular be constructed as a soft iron deep-drawn part. A plurality ofpermanent magnetic segments or a one-part permanent magnet 69 are fixedto the inner face of shielding can 26 radially facing the statorlamination 48. The permanent magnet 69 preferably comprises a mixture ofhard ferrite, for example, barium ferrite, and an elastic material.Thus, it is a so-called rubber magnet. The latter is trapezoidally orapproximately trapezoidally magnetized via the pole pitch in a motorconstruction having a relatively small pole clearance. At the same time,the shielding can 26 forms the magnetic return path for magnet 69. Theshielding can 26 surrounds the magnetically active parts 48, 49, 69 ofthe driving motor 45 on the periphery thereof, as well as on one endthereof. The bottom 28 of shielding can 26 is adapted to the shape ofthe coil winding heads 27 of the stator winding 49 and contains acentral opening 29, whose edge is in the immediate radial vicinity ofthe circumferential surface of the bearing tube 50. In this way, theshielding can effectively prevents the magnetic flux from strayingtowards the outside of the storage disk receiving part 25.

The storage disk receiving part 25 has two stepped stages 74 and 75,each of whose circumferential surfaces in the present embodiment carry aplurality of radially distributed and projecting bearing webs 79 or 80.The outsides of bearing webs 79, 80 are ground in a dimensionally truemanner to accommodate the internal diameter of the hard storage disks tobe placed on the receiving part 25. The stepped stages 74, 75 formshoulders 81, 82 and are provided respectively with an annular recess 83and 84 at the foot axially of bearing webs 79, 80. This structureensures that storage disks mounted on the bearings webs 79, 80, andhaving either one of two opening diameters, will cleanly engage againsteither the shoulder 81 or 82.

The assembly flange 24 is provided with a recess 85 in which is housed aprinted circuit board 86. This printed circuit board carries a rotaryposition detector, for example a Hall IC, as well as other circuitcomponents for the control and regulation of the driving motor 45. TheHall IC 63 extends up axially from the circuit board 86 to the immediatevicinity of the stator lamination 48. The permanent magnet 69 projectsaxially over the stator lamination 48 in the direction of circuit board86 until it partly overlaps the Hall IC 63. In this way, the Hall IC 63or, if desired, some other magnetic field-dependent semi-conductorcomponent, determines the rotary position of the rotor of the drivingmotor 45.

In the illustrated embodiment, the two bearings 52, 53 are spacedapproximately the same axial distance from the axial center of thepermanent magnet 69 and the stator lamination 48.

Disk storages are most usually operated in "clean room" environments toprotect them against contaminants. By means of the assembly flange 24,the storage drive is arranged on a partition (not shown) which separatesthe ultra-clean area for receiving the storage disks from the remainderof the interior of the equipment. Dirt particles, grease vapors and thelike from bearing 52 and parts of the driving motor 45 are preventedfrom passing into the storage disk receiving area by labyrinth seals 90and 91. The labyrinth seal 90 is formed in that the end of the bearingtube 50 away from the assembly flange 24 that projects into an annularslot 87 on the inside of the storage disk receiving part 25, accompaniedby the formation of sealing gaps. Similarly, for forming the labyrinthseal 91, the end of the shield can 26 projects into the annular slot 88of the assembly flange 24. The labyrinth seals 90, 91 are preferablydimensioned in the manner described in the aforementioned U.S. Pat. No.4,438,542.

The embodiment of FIG. 3 differs from the arrangement according to FIGS.1 and 2 in that storage disks having the same opening diameters areplaced on bearing webs 79 of a storage disk receiving part 89, whichsurrounds the majority of the axial dimension of the magnetic shieldingcan 26. In other words, the magnetically active parts 48, 49, 69 of thedriving motor 45 are partially located within the central opening of thestorage disk. A bush-like hub 98 is pressed or cast into the storagedisk receiving part 89. The rotor shaft 46 is then pressed into the hub98. The edge of the central opening 29 in the bottom 28 of the shieldingcan 26 extends up to the portion 99 of the receiving part 89 whichreceived the hub 98.

The bearing tube 50 projects in the axial direction on the side of theassembly flange 100 remote from the stator lamination 48. As a result, aparticularly large axial spacing between the two bearings 52, 53 can beachieved. Axially, bearing 52 is in the vicinity of the axial center ofthe permanent magnet 69 and of the stator lamination 48. The axialspacing between bearing 52 and 53 is equal to or larger than double thebearing external diameter. To prevent electrical charging of the rotorwhich in operation rotates at high speed and which would disturb theoperational reliability of the disk storage device, the rotor shaft 46is electrically conductively connected to the equipment chassis by meansof a bearing ball 78 and a spring contact (not shown). The printedcircuit board 101, carrying the rotary position detector 63 and theother electronic components, is supported on the end of a spacer ring102 facing an assembly flange 100 and is located between the flange andthe stator lamination 48. An annular slot 103 is formed in assemblyflange 100 and is aligned with the annular circuit board 101. Theannular slot 103 provides space for receiving the wire ends and solderedconnections projecting from the underside of the circuit board 101.

FIG. 4 shows an embodiment in which a storage disk receiving part 105 isaxially extended in order to be able to house a larger number of storagedisks than in the arrangement of FIG. 3. The bearing tube 50 iscorrespondingly axially extended in order to be able to use the existinginstallation space with a view to a maximum axial spacing between thebearings 52 and 53. The end of the bearing tube 50, remote from asassembly flange 106, embraces the hub 98 connecting the receiving part105 and the shaft 46, accompanied by the formation of a labyrinth seal107. The edge of the central opening 29 of shielding can 26 extends upclose to the outside of the bearing tube 50. The free end of theshielding can 26 engages a recess 108 in the assembly flange 106. As aresult, a further labyrinth seal 109 is formed. This embodimentotherwise corresponds to the structures described hereinbefore.

In a further development of the invention where a disk storage driveutilizes a brushless D.C. drive motor having a stator provided with awinding and an external rotor coaxially surrounding the stator andspaced therefrom by a substantially cylindrical air gap, the rotorincludes a permanent magnetic rotor magnet and a soft magnetic yoke. Themotor further includes a hub concentric to the yoke and connected to therotor for rotation therewith. The hub has a disk mounting or supportportion, which extends through the central opening of the storage diskand receives at least one storage disk in a clean area space or chamberof a storage drive.

In known disk storage drives of this type there is a hub or armaturesleeve for receiving the storage disk or disks wherein the disk mountingportion extends over a small part of the axial dimension of themagnetically active stator and rotor parts, i.e. the stator winding andthe rotor magnet that interacts therewith.

In disk storage units, there is an increasing need for reducing thespace requirement for the storage unit. Thus, another problem of theinvention is to provide a disk storage drive that takes up particularlylittle space and consequently allows a minimization of the disk storagedimensions.

According to a further aspect of the invention, this problem is solvedby the stator winding and the rotor magnet interacting therewith, atleast with respect to half their axial dimension, being housed withinthe area surrounded by the disk mounting portion of the hub. Themagnetically active parts of the drive motor in this construction arelocated mostly within the space which is already required for holdingthe storage disks, particularly magnetic rigid storage disks, but alsostorage disks of other types, e.g. optical storage disks.

Preferably, the stator winding and the motor magnet interactingtherewith are contained within the space surrounded by the disk mountingportion of the hub by up to 2/3 of their axial dimension. A particularlyspace-saving overall arrangement is obtained if the magnetically activestator and rotor parts are located substantially completely within thisspace.

The diameter of the central opening of the storage disks, e.g. magneticrigid storage disks, is standardized and consequently its size ispredetermined by industry and the market to a fixed value. However, theapplication of the drive energy requires a certain motor size. Theconditions are particularly critical in known small storage disks with acentral opening diameter of, for example, only 25 mm. In order toprovide maximum space for the magnetically active motor parts in thediametrically limited area of the storage disk central opening,according to even a further development of the invention, the wallthickness of the disk mounting portion of the hub is minimizedconsistent with needed mechanical strength. The wall thickness of thedisk mounting portion is approximately the same as and preferablysmaller than the wall thickness of the part of the magnetic yoke whichis concentric thereto.

The disk mounting portion preferably has a cylindrical outer peripheralsurface, that is, a peripheral surface free from bearing webs or ribs inproviding a maximum cross section while taking into account the fixeddiameter of the central opening of the storage disks consistent with thenecessary mechanical strength of the hub.

At least those surface parts of the hub located in the clean area orchamber of the drive must not give off, even during prolonged use of thedisk storage drive, significant quantity of dirt particles, for example,from oxidation. Preferably, the hub is made from a material which, evenafter cutting, is suitable for use in a clean area or chamber, that is,a material which after being cut, and without a corrosion-inhibitingtreatment following the cutting, meets the strict cleanness conditionsnecessary with disk storage drives in the clean chamber of the drivesreceiving the storage disks. Such a construction makes it possible tofinish, for example, by grinding or otherwise stripping the outerperipheral surface of the disk support portion after assembly of the huband the drive motor with respect to the centricity with the rotationaxis. Such metal finishing of the installed hub is frequently necessaryin order to fulfil the extreme demands in connection with disk storagedrives with respect to accuracy of rotation or minimization ofuntrueness of the hub. It is particularly appropriate to have a hub madefrom light metal, preferably aluminum or an aluminum alloy. Light metalhubs can be used in clean chambers without further treatment, even aftercutting has taken place. For example, by using a diamond tool, and whilerespecting the necessary precision, such hubs can be stripped in a lessexpensive way than by grinding, particularly the disk mounting portionwith a cylindrical outer circumferential surface. The hub is preferablyimpact extruded or cast and is pressed hot on the magnetic yoke. Inprinciple, other possibilities for joining hub and yoke exist, such as abonding together of the two parts.

The magnetic yoke can have a cup or pot-shaped construction as is known.It is more advantageous, however, to provide an annular magnetic yokeand approximately insert a magnetic shield ring in the hub extendingradially inwardly substantially from the clean chamber axial end of theannular magnetic yoke. As a result, necessary guidance of the magneticflux and efficient magnetic shielding of the storage disks with respectto the drive motor are achieved. The combination of yoke ring and shieldring can be produced less expensively than a cup or pot. The shield ringcan be relatively thin so that the overall axial size of the drive canbe further reduced, or, for a constant axial size, provide more spacefor a hub end wall at the closed end of the subassembly comprising thehub, magnetic yoke and motor magnet. The magnetic yoke can beappropriately constructed as a rolled ring, particularly a steel ring,or as a portion of a tube.

The rotor and the hub can be fixed to a shaft which is supported in abearing system at least partly housed within the drive motor stator. Abearing bush receiving the shaft can be shaped on to the yoke, if theyoke is constructed in cup-shaped manner, or preferably on to the hub.This obviates a separate component of the bush. The rotor and the hubcan, according to a modified construction, be mounted to rotate togethervia a bearing system of a fixed shaft, the leads of the stator windingpassing through the fixed shaft to the outside of the drive.

A control magnet, for example, in the form of a control magnet ring, ispreferably connected to the unit that includes the rotor and the hub,the magnet interacting with a stationary magnetic field-sensitiverotation position sensor whose function is to produce commutatingcontrol signals and optionally additional control signals, such as apulse for a given rotor reference position. The control magnet isappropriately located on the axially open side of the unit that includesthe rotor and hub. It can be axially aligned with the rotor magnet. Therotor magnet can optionally serve as the control magnet. The rotationposition sensor is advantageously placed on a printed circuit boardaxially facing the axially open side of the unit comprising the rotorand hub.

In FIGS. 5 and 6, the drive motor 118 has a stator 119 with a statorlamination bundle 110. The bundle 110 is radially symmetrical withrespect to a central rotation axis 110A and is provided with an annularcentral portion 110B. The stator laminations 110 form six stator poles111A to 111F, each of which, in the plan view according to FIG. 5, has asubstantially T-shaped configuration. The stator poles are positionedwith a reciprocal angular distance of 60°. A sintered iron core can beprovided in place of a bundle of laminations. Pole shoes 112A to 112F ofthe stator poles together with a permanent magnetic motor magnet 113define a substantially cylindrical air gap 114. In the manner indicatedin FIG. 5, motor magnet 113 is radially magnetized in quadripolar mannerin the circumferential direction, that is, it has four portions 113A to113D and on the inside of the annular motor magnet 113 facing the airgap 114 are provided in alternating sequence two magnetic north polesand two magnetic south poles 115, 116. In the illustrated embodiment,each of the poles 115 and 116 have a width of substantially 180° el,(corresponding to 90° mechanical). Thus, an approximately rectangular ortrapezoidal magnetization is obtained in the circumferential directionof the air gap 114.

The motor magnet 113 is fitted in a soft magnetic material externalrotor cup or pot 117 serving as a magnetic yoke and has a magneticshield bonded thereinto. The cup 117 and the magnet 113 together form anexternal rotor 130. The external rotor cup 117 has an end wall 117A(FIG. 6) and a cylindrical circumferential wall 117B. The motor magnet113 can be a rubber magnet, or a plastic-bonded magnet. In place of aone-part magnet ring, dish-shaped magnet segments can be bonded or insome other way fixed into the cup 117. Particularly suitable materialsfor the magnet ring or segments are magnetic material in a syntheticbinder, a mixture of hard ferrite and elastomeric material, ceramicmagnetic material or samarium cobalt. While in the representedembodiment each of the poles extends over substantially 180° el, it isalso possible to work with narrower poles. The rotor pole width,however, should be at least 120° el to obtain a high motor output.

Together the stator poles 111A to 111F define six stator slots 120A to120F, in which is placed a three-strand stator winding. Each of thethree strands includes two 120° el-cored coils 121,122; 123,124; and125,126. Each is wound around one of the stator poles 111A to 111F. Thetwo coils in series of each strand diametrically face one another, asshown in FIG. 5. The coils are preferably wound in bifilar manner (notshown). As can be gathered from the diagrammatic representation of FIG.5, any overlap between coils 121 to 126 is avoided and in this wayparticularly short coil winding heads 127 (FIG. 6) are obtained. Theslot openings 128A to 128F can be between 3° el and 30° el. In thepresent stator winding configuration, slots 120A to 120F can beexcellently filled. There is generally no need to provide caps for theslot openings 128A to 128F.

The present motor design makes it possible to obtain a relatively largehole 129 within the stator, because the depth of the stator slots 120Ato 120F can be kept relatively small. It is easy to obtain ratiosbetween the diameter I of internal hole 129 and the stator externaldiameter E of the pole shoes 112 of at least 0.35. Preferably, the I/Evalue is in the range 0.4 to 0.7. The L/E ratio between the axial lengthL (FIG. 6) of the stator iron and the stator external diameter E ispreferably equal to or smaller than 1. These dimensioning ratios are ofparticular significance in connection with a stable mounting of therotor. This is of particular importance in connection with drives fordisk storage systems. In addition, the overall resistance of the statorwinding is kept particularly small.

For the purpose of the mounting of the rotor 130, according to FIG. 6 inthe center of the external rotor cup 117 is fixed a stub shaft 132 via abearing bush 131 shaped on to the cup, the shaft being supported viaaxially spaced ball bearings 133 in a cylindrical sleeve 134, which alsocarries the stator laminations 110 and is fixed to an assembly flange135.

A preferably light metal hub 137 (FIG. 6) for a rigid disk is providedwith a cylindrical disk mounting portion 136 and is placed, for example,by shrinking onto the external rotor cup 117. One or more rigid storagedisks 139, preferably magnetic disks, are placed on the disk mountingportion 136. The disk mounting portion extends through a central opening140 in the storage disks 139, which are reciprocally axially spaced byspacers 141 and are fixed with respect to the hub 137 by a knownclamping device. In the embodiment shown in FIG. 6, somewhat more than2/3 of the axial dimension of the magnetically active stator and rotorparts of drive motor 118, that is, the motor magnet 113 and the statorwindings 121 to 126 project into a space or volume 146 surrounded by thedisk mounting portion 136. The wall thickness of the disk mountingportion 136 of the hub 37 is smaller than the wall thickness of thecylindrical circumferential wall 117B of the cup 117 that forms themagnetic yoke, so that a maximum cross section is made available for therotor parts 113, 117, 119 in the predetermined central opening 140. Inparticular, the wall thickness of the disk support portion 136 is madeas small as possible consistent with mechanical strength requirements.To increase the dimensional stability of the hub 137, near the open endof the unit that includes the hub 137, the external rotor cup 117 andthe motor magnet 113, the hub carries a thickened, outwardly radiallyprojecting flange 147, which simultaneously axially supports the rigidstorage disk 139 closest to the flange.

The hub 137, together with the storage disks 139 supported thereon, islocated in a clean chamber 149, defined by the disk storage casingparts. The assembly flange 135 forms part of the clean chamber boundarytowards the lower side in FIG. 6. The upper bearing 113 in FIG. 6 islocated between a shoulder 151 on the sleeve 134 and a spacing ring 152,whose side remote from the bearing 133 engages the bottom surface of thebearing bush 131. The stub shaft 132 is convex at its lower end 153 andis approximately mounted in an axial bearing (not shown). Close to thelower end 153, a fastening ring 155 is arranged in an annular slot 154of the shaft 132. Against the upper surface of the ring bear two cupsprings 156, which engage on an intermediate ring 157. The lower ballbearing 153 is positioned between the intermediate ring 157 and afurther shoulder 158 of the sleeve 134.

The assembly flange 135 carries a circuit board 138, which canoptionally carry the commutating electronics and/or other circuitcomponents, such as for speed regulation. The circuit board 130 moreparticularly carries three rotation position sensors 142, 143, 144. Inthe illustrated embodiment, they are magnetic field sensors, such asHall generators, field plates, magnetic diodes and the like.Bistable-switching Hall IC's are particularly advantageous. The use of180° el wide rotor poles 115, 116 makes it possible to use the motormagnet 113 as the control magnet of the position sensors 142, 143, 144.The embodiment according to FIG. 6 shows the rotation position sensors142, 143, 144 (of which only sensor 142 is seen) axially facing themagnet 113 controlling them. It is also possible to arrange the rotationposition sensors in the manner indicated in broken line form in FIG. 6to radially face the magnet 113 controlling them. The rotation positionsensors 142, 143, 144 are appropriately so peripherally positioned withrespect to the coils 121 to 126 that changes to the sensor switchingstates substantially coincide with the zero crossings of the associatedcoil voltages. In the embodiment according to FIG. 5 this is achieved inthat the rotation position sensors are displaced by 15° mechanical withrespect to the center of the slot openings 128A, 128B, 128C.

The embodiment according to FIG. 7 essentially differs from thataccording to FIG. 6 in that a control magnet 145 separate from the motormagnet 113 is provided for energizing the rotation position sensors 142,143, 144. The control magnet 145 is located radially outside the motormagnet 113 on the bottom of a flange 117C, which projects radiallyoutwardly from the peripheral wall 117B of the external rotor cup 117,on its open end. The external rotor cup 117 and the hub 137' terminatein a flush manner at the open end in the embodiment of FIG. 7. At 159 isindicated a connection of one of the coils 121, 126 to a contact of theprinted circuit board 138 which extends outwardly through an opening 161in the assembly flange 135, a connecting cable 160.

FIG. 8 illustrates another embodiment of the disk storage drive inwhich, differing from the embodiment of FIGS. 6 and 7, a hub 164corresponding to the hub 137 has an end wall 164A engaging the end wall117B of the external rotor cup 117. A bearing bush 165 for the shaft 132is formed integrally in the end wall 164A. On the end of the disksupport portion 166 of the hub 164 remote from the end wall 164A islocated a radially outwardly bent flange 167, which passes into acircumferential wall 168 concentric to, but having a larger diameterthan, the disk mounting portion 166. The circumferential wall 168engages radially and externally over the flange 117C of the cup 117. Thejunction between the flange 117C and the circumferential wall 168 issealed in the manner indicated at 169 by varnish, adhesive or the like.Thus, as in FIG. 7, it is ensured that dirt particles are not passedradially outwardly from the flange 117C and into the clean chamber 149.The control magnet 145 interacting with the rotation position sensors(of which only sensor 142 is shown in FIG. 8) is axially aligned withthe motor magnet 113 and is fitted to the side of the magnet 113 remotefrom the end wall 117A. The external rotor cup 117 is drawn down to suchan extent in FIG. 8 that it surrounds the control magnet 145. The spaceleft free between the end wall 117A and the end of the magnet 113 facingthe wall is filled with an adhesive or some other filling material 170.The bearing system for the shaft 132 formed by the two ball bearings 133is sealed with respect to the inner area of the motor and consequentlywith respect to the clean chamber 149 by means of a magnetic fluid seal172, which comprises two annular pole pieces 173, 174, a permanentmagnet ring 175 located between these pole pieces and a magnetic fluid(not shown), which fluid is introduced into an annular clearance 176between the magnetic ring 175 and a portion 177 of the shaft 132. Sealsof this type are known as "ferro-fluidic seals". The seal 172effectively prevents the passage of dust particles from the bearingsystem into the clean chamber 149. The seal 172 is adjacent to, butaxially spaced from, the bearing bush 165, which ensures that magneticfluid is not drawn by capillary action out of the seal 172.

As can be gathered from FIG. 8, the magnetically active stator and rotorparts are substantially completely housed within the space enclosed bythe disk support portion 166. FIG. 8 also shows an axial bearing 179 forthe shaft 132. The bearing 179 is located on a spring clip 180, which isin turn placed on a cover 181 introduced into the end of a sleeve 182remote from the clean chamber 49. Similarly to the sleeve 134 of theembodiment according to FIGS. 6 and 7, the sleeve 182 receives thebearings 133, but is connected in one piece with the assembly flange 183corresponding to the assembly flange 135.

Similarly to the spring clip 180, the axial bearing 179 is preferablyelectrically conducting. This makes possible the elimination ofelectrostatic charges of the shaft 132 via the bearing 179 in the springclip 180.

The circuit board 138 is connected to the assembly flange 183 via anadhesive coating 184, which is located in a slot 185 of the assemblyflange 183. To further reduce the overall axial height of the diskstorage drive, the circuit board 138 is provided with openings 186 inthe vicinity of the rotation position sensors, and the rotation positionsensors are introduced into the slot 185 and the openings 186. Near theengagement point between the upper pole piece 173 and the innercircumferential wall 187 of the sleeve 182, an additional seal by meansof coating lacquer or the like is provided at 188.

The embodiment according to FIG. 9 is similar to that of FIG. 8. Thebearing bush 131, however, is formed integrally in the end wall 117A ofthe external rotor cup 117, which acts as a magnetic shield. The endwall 117A contains three threaded holes 190, which are circumferentiallydisplaced from one another by 120°. The holes 190 are used for fittingthe earlier mentioned but not shown clamping device for the rigidstorage disks 139 (FIG. 6). Under the end wall 117A is located a coverring 191 which seals the inner area of the motor relative to the cleanchamber 149 near the threaded holes 190. Most of the axial length of themagnetically active stator and rotor parts of the drive motor are onceagain located in the area 146, which is surrounded by the disk supportportion 136' of the hub 137' similar to that shown in FIG. 7.

FIG. 10 shows a further modified embodiment of the invention, whichessentially differs from the previous constructions of FIGS. 5-9 in thatthe external rotor cup 117 is replaced by a soft magnetic yoke ring 194and a separate soft magnetic shield ring 195. The shield ring 195extends from the clean chamber-side axial end 196 of the yoke ring 194in a radially inwardly direction. The wall thickness of the shield ring195 can be much less than that of the yoke ring 194. Threaded holes 197functionally corresponding to the threaded holes 190 of FIG. 9 areformed in the end wall 198 of a hub 199, in which integrally is formedthe bearing bush 1100 for the shaft 132. Near the threaded holes 197, ashield ring 195 is provided with depressions 1101, which depressionspermit the use of the full thread length of the threaded holes 197.Filling material 170 is provided in the space between the upper end ofthe motor magnet 113 in FIG. 10, the end 196 of the yoke 194 and theradially outer part of the shield ring 195. The magnetically activerotor and stator parts are more than 2/3 located in the area surroundedby the cylindrical disk support portion 1102 of the hub 199.

The yoke ring 194 can be a rolled ring, particularly a steel ring, or aportion of a tube. Manufacture is simplified compared with the use of anexternal rotor cup 117. In addition, additional axial length is saved,because on the one hand the wall thickness of the shield ring 195 can bekept small, and because on the other hand no space is lost, consideringthe way in which some space is required when using the cup 117 with itsradius r (FIG. 9) at the transition point between its circumferentialwall 117B and its end wall 117A. The axial construction space which thushas been made available can be used to give the end wall 198 a greaterthickness and consequently increase the length of the threaded holes197.

Whereas in the case of the embodiment according to FIGS. 5 to 10, theshaft 132 rotates in operation, FIGS. 11 and 12 illustrate embodimentswith a stationary shaft 1105. According to FIG. 11, the shaft 1105 isfitted into the disk storage device. By means of a first ball bearing1106, a hub 1107 is mounted to rotate on the shaft 1106. The hub 1107has an end wall 1108 with a formed-in bearing bush 1109, a disk supportportion 1110 and, on the side remote from end wall 1108, a radiallyoutwardly projecting reinforcing flange 1111. The hub 1107 is connectedto a soft magnetic yoke ring 194. The soft magnetic shield ring 195engages the inside of the end wall 1108. The circuit board 138 with therotation position sensors, of which only the sensor 142 is shown in FIG.11, is suspended by means of supports 1112 (FIG. 12) on the statorlaminations 110. A motor cover 1114 is mounted by means of a second ballbearing 1113 on the shaft 1105, the cover tightly sealing the motor onthe axial end remote from the end wall 1108. A magnetic fluid orferrofluidic seal 172 or 172' discussed in detail relative to FIG. 8, isprovided on each of the outside of the bearings 1106, 1113. The seals172, 172' ensure a sealing of the bearing system with respect to theclean chamber 149, so that the complete drive motor can be located inthe clean chamber. The connections of the stator winding and/or theelectronic components mounted on the circuit board 138 can be led out bymeans of a cable 1115, which is placed in an axial slot 1116 of theshaft 1105.

The embodiment of FIG. 12 differs from that of FIG. 11 substantially inthat in place of the shield ring 195 and the yoke ring 194 there is aone-piece soft magnetic material cup 1117 with an end wall 1117A and acircumferential wall 1117B corresponding to the cup 117.

In the embodiments according to FIGS. 11 and 12, the magnetically activestator and rotor parts of the drive motor are located within the areasurrounded by the disk mounting portion 1110.

It should be apparent that certain constructional features areinterchangeable in all the illustrated embodiments.

What is claimed is:
 1. A disk storage drive comprising:a clean chamberfor housing a storage disk; a brushless drive motor having a stator anda winding on the stator, the stator having an axial longitudinaldimension and the winding having a pair of opposed end surfaces; anexternal rotor having a rotation axis and coaxially surrounding thestator, an inner wall of said rotor being spaced from said stator by asubstantially cyclindrical air gap, said rotor having a permanent magnetwith an axial longitudinal dimension and a soft magnetic yoke with anaxially extending wall portion and a radially extending wall portion,said permanent magnet forming the inner wall of said rotor adjacent theair gap; a hub held fast on the rotor for rotation therewith and beingcoaxial to the yoke, said hub having a machinable outer surface andbeing made of a non-ferromagnetic, non-corrodible material suitable foruse in a clean chamber following machining of the outer surface; anouter peripheral cylindrical surface on said hub dimensioned to passthrough a standardized central opening of a storage disk for receivingand mounting the storage disk for rotation therewith in said cleanchamber, said outer peripheral cylindrical surface radially enclosingsaid soft magnetic yoke of said rotor and said stator for a substantialpart of the axial extensions thereof, and at least half of the axiallongitudinal dimension of the stator winding and of the rotor magnetinteracting magnetically therewith being housed within said outerperipheral cylindrical surface of the storage disk mounting portion ofthe hub, and said yoke radial wall portion extending radially inwardlyfrom one axial end of the yoke axial wall portion by a distancesufficient to extend over the adjacent one of said pair of winding endsurfaces.
 2. A disk storage drive as claimed in claim 1, wherein atleast two-thirds of said axial longitudinal dimension of the statorwinding and of the rotor magnet interacting magnetically therewith ishoused within the disk mounting portion of the hub.
 3. A disk storagedrive as claimed in claim 2, wherein the stator winding and the rotormagnet interacting therewith are substantially completely housed withinthe disk mounting portion of the hub.
 4. A disk storage drive as claimedin claim 1, wherein the wall of the disk mounting portion is no thickerthan the wall of the part of the magnetic yoke coaxial therewith.
 5. Adisk storage drive as claimed in claim 4, wherein the disk supportmounting wall is thinner than said yoke wall.
 6. A disk storage drive asclaimed in claim 1, wherein the hub is made from light metal.
 7. A diskstorage drive as claimed in claim 1, wherein the externalcircumferential surface of the disk mounting portion of the hub, afterassembly of hub and drive motor, is finished with respect to centricitywith the rotation axis.
 8. A disk storage drive as claimed in claim 7,wherein said surface is ground or turned to finish.
 9. A disk storagedrive as claimed in claim 1, wherein the hub is extruded or cast.
 10. Adisk storage drive as claimed in claim 1, wherein the hub is pressed hoton the magnetic yoke.
 11. A disk storage drive as claimed in claim 1,wherein the magnetic yoke is annular.
 12. A disk storage drive asclaimed in claim 11, wherein a magnetic shield ring is placed in the huband extends from the inside wall of the hub radially inwardly andsubstantially from one axial end of the annular yoke.
 13. A disk storagedrive as claimed in claim 1, wherein the rotor and the hub are fixed toa shaft rotatably supported axially in a bearing system that is at leastpartly housed within the stator of the drive motor.
 14. A disk storagedrive as claimed in claim 13, wherein a bearing bush receiving the shaftis formed integrally in the hub or the magnetic yoke.
 15. A disk storagedrive as claimed in claim 14, wherein the bearing system is sealed bymeans of at least one magnetic fluid or ferro-fluidic seal.
 16. A diskstorage drive as claimed in claim 15, wherein the magnetic fluid orferro-fluidic seal is positioned adjacent to but axially spaced from thebearing bush.
 17. A disk storage drive as claimed in claim 1, whereinthe rotor and the hub are rotatably mounted by means of a bearing systemon a fixed shaft.
 18. A disk storage drive as claimed in claim 17,wherein leads are provided for the stator winding that pass through thefixed shaft to the outside of the drive.
 19. A disk storage drive asclaimed in claim 1, wherein a control magnet is connected to the unitthat includes the rotor and hub, and interacts with a stationary,magnetic field-sensitive rotation position sensor.
 20. A disk storagedrive as claimed in claim 19, wherein the control magnet is positionedon that side of the unit that includes the rotor and hub and that isopen in the axial direction.
 21. A disk storage drive as claimed inclaim 19, wherein the control magnet is axially aligned with the rotormagnet.
 22. A disk storage drive as claimed in claim 19, wherein therotation position sensor is mounted on a printed circuit board thataxially faces the side of the unit that includes the rotor and hub andthat is open in the axial direction.
 23. A disk storage drive as claimedin claim 1, wherein the ratio of inner and outer diameters of the statoris at least 0.35.
 24. A disk storage drive as claimed in claim 23,wherein said ratio is 0.4 to 0.7.
 25. A disk storage drive as claimed inclaim 1, wherein the ratio of axial length to external diameter of thestator does not exceed
 1. 26. A disk storage drive comprising:a cleanchamber for housing a storage disk; a brushless drive motor having astator and a winding on the stator, the stator having an axiallongitudinal dimension; an external rotor having a rotation axis andcoaxially surrounding the stator, an inner wall of said rotor beingspaced from said stator by a substantially cylindrical air gap, saidrotor having a permanent magnet with an axial longitudinal dimension anda soft magnetic annular yoke with an axially extending wall portion,said permanent magnet forming the inner wall of said rotor adjacent theair gap; a hub held fast on the rotor for rotation therewith and beingcoaxial to the yoke, said hub having a machinable outer surface andbeing made of a non-ferromagnetic, non-corrodible material suitable foruse in a clean chamber following machining of the outer surface; anouter peripheral cylindrical surface on said hub dimensioned to passthrough a standardied central opening of a storage disk for receivingand mounting the storage disk for rotation therewith in said cleanchamber, said outer peripheral cylindrical surface radially enclosingsaid soft magnetic yoke of said rotor and said stator for a substantialpart of the axial extensions thereof, and at least half of the axiallongitudinal dimension of the stator winding and of the rotor magnetinteracting magnetically there with being housed within said outerperipheral cylindrical surface of the storage disk mounting portion ofthe hub; and a magnetic shield ring located in the hub and extendingfrom the inside wall of the hub radially inwardly and substantially fromone axial end of the annular yoke. .Iadd.
 27. A disk storage drivecomprising:a clean chamber for housing a storage disk; a brushless drivemotor having a stator and a winding on the stator, the stator having anaxial longitudinal dimension; an external rotor having a rotation axisand coaxially surrounding the stator, an inner wall of said rotor beingspaced from said stator by a substantially cylindrical air gap, saidrotor having a permanent magnet with an axial longitudinal dimension anda soft magnetic annular yoke with an axially extending wall portion,said permanent magnet forming the inner wall of said rotor adjacent theair gap; a hub held fast on the rotor for rotation therewith and beingcoaxial to the yoke, said hub having a machinable outer surface andbeing made of a non-ferromagnetic, non-corrodible material suitable foruse in a clean chamber following machining of the outer surface; anouter peripheral cylindrical surface on said hub dimensioned to passthrough a standardized central opening of a storage disk for receivingand mounting the storage disk for rotation therewith in said cleanchamber, said outer peripheral cylindrical surface radially enclosingsaid soft magnetic annular yoke of said rotor and said stator for asubstantial part of the axial extensions thereof, and at least half ofthe axial longitudinal dimension of the stator winding and of the rotormagnet interacting magnetically therewith being housed within said outerperipheral cylindrical surface of the storage disk mounting portion ofthe hub, and a magnetic shield ring located in the hub and extendingsubstantially from the soft magnetic annular yoke radially inwardly andsubstantially from one axial end of the soft magnetic annularyoke..Iaddend. .Iadd.28. A disk storage drive as claimed in claim 27,wherein the stator winding and the rotor magnet interacting therewithare substantially completely housed within the disk mounting portion ofthe hub..Iaddend. .Iadd.29. A disk storage drive as claimed in claim 27,wherein the wall of the disk mounting portion is no thicker than thewall of the part of the soft magnetic annular yoke coaxialtherewith..Iaddend. .Iadd.30. A disk storage drive as claimed in claim29, wherein the disk support mounting wall is thinner than the wall ofthe soft magnetic annular yoke..Iaddend. .Iadd.31. A disk storage driveas claimed in claim 27, wherein the hub is made from lightmetal..Iaddend. .Iadd.32. A disk storage drive as claimed in claim 27,wherein the external circumferential surface of the disk mountingportion of the hub, after assembly of hub and drive motor, is finishedwith respect to centricity with the rotation axis..Iaddend. .Iadd.33. Adisk storage drive as claimed in claim 32, wherein said surface isground or turned to finish..Iaddend. .Iadd.34. A disk storage drive asclaimed in claim 27, wherein the hub is extruded or cast..Iaddend..Iadd.35. A disk storage drive as claimed in claim 27, wherein the hubis pressed hot on the soft magnetic annular yoke..Iaddend. .Iadd.36. Adisk storage drive as claimed in claim 27, wherein the rotor and the hubare fixed to a rotatable shaft..Iaddend. .Iadd.37. A disk storage driveas claimed in claim 27, wherein the rotor and the hub are fixed to ashaft rotatably supported axially in a bearing system that is at leastpartly housed within the stator of the drive motor..Iaddend. .Iadd.38. Adisk storage drive as claimed in claim 27, wherein a bearing bushreceiving the shaft is formed integrally in the hub or soft magneticannular yoke..Iaddend. .Iadd.39. A disk storage drive as claimed inclaim 38, wherein the bearing system is sealed by means of at least onemagnetic fluid or ferrofluidic seal..Iaddend. .Iadd.40. A disk storagedrive as claimed in claim 39, wherein the magnetic fluid or ferrofluidicseal is positioned adjacent to but axially spaced from the bearingbush..Iaddend. .Iadd.41. A disk storage drive as claimed in claim 27,wherein the rotor and the hub are rotatably mounted by means of abearing system on a fixed shaft..Iaddend. .Iadd.42. A disk storage driveas claimed in claim 41, wherein leads are provided for the statorwinding that pass through the fixed shaft to the outside of thedrive..Iaddend. .Iadd.43. A disk storage drive as claimed in claim 27,wherein a control magnet is connected to the unit that includes therotor and the hub, and interacts with a stationary magnetic positionsensor..Iaddend. .Iadd.44. A disk storage drive as claimed in claim 43,wherein the control magnet is positioned on that side of the unit thatincludes the rotor and the hub and that is open in the axialdirection..Iaddend. .Iadd.45. A disk storage drive as claimed in claim43, wherein the control magnet is axially aligned with the rotormagnet..Iaddend. .Iadd.46. A disk storage drive as claimed in claim 43,wherein the rotation position sensor is mounted on a printed circuitboard that axially faces the side of the unit that includes the rotorand the hub and that is open in the axial direction..Iaddend. .Iadd.47.A disk storage drive as claimed in claim 27, wherein the ratio of innerand outer diameters of the stator is at least 0.35..Iaddend. .Iadd.48. Adisk storage drive as claimed in claim 47, wherein said ratio is 0.4 to0.7..Iaddend. .Iadd.49. A disk storage drive as claimed in claim 27,wherein the ratio of axial length to external diameter of the statordoes not exceed 1..Iaddend. .Iadd.50. A disk storage drive comprising:aclean chamber for housing a storage disk; a brushless drive motor havinga stator and a winding on the stator, the stator having an axiallongitudinal dimension; an external rotor having a rotation axis andcoaxially surrounding the stator, the rotor being fixed to a shaftrotatably supported axially in a bearing system that is at least partlyhoused within the stator, an inner wall of said rotor being spaced fromsaid stator by a substantially cylindrical air gap, said rotor having apermanent magnet with an axial longitudinal dimension and a softmagnetic annular yoke with an axially extending wall portion, saidpermanent magnet forming the inner wall of said rotor adjacent the airgap; a hub held fast on the rotor for rotation therewith and beingcoaxial to the yoke, said hub having a machinable outer surface andbeing made of a non-ferromagnetic, non-corrodible material suitable foruse in a clean chamber following machining of the outer surface; anouter peripheral cylindrical surface on said hub dimensioned to passthrough a standardized central opening of a storage disk for receivingand mounting the storage disk for rotation therewith in said cleanchamber, said outer peripheral cylindrical surface radially enclosingsaid soft magnetic annular yoke of said rotor and said stator for asubstantial part of the axial extensions thereof, and at least half ofthe axial longitudinal dimension of the stator winding and of the rotormagnet interacting magnetically therewith being housed within said outerperipheral cylindrical surface of the storage disk mounting portion ofthe hub, and a magnetic shield ring located in the hub and extendingsubstantially from the soft magnetic annular yoke radially inwardly andsubstantially from one axial end of the soft magnetic annular yoke..Iadd.51. A disk storage drive comprising: a clean chamber for housing astorage disk; a brushless drive motor having a stator and a winding onthe stator, the stator having an axial longitudinal dimension; anexternal rotor having a rotation axis and coaxially surrounding thestator, the rotor being rotatably mounted by means of a bearing systemon a fixed shaft, an inner wall of said rotor being spaced from saidstator by a substantially cylindrical air gap, said rotor having apermanent magnet with an axial longitudinal dimension and a softmagnetic annular yoke with an axially extending wall portion, saidpermanent magnet forming the inner wall of said rotor adjacent the airgap; a hub held fast on the rotor for rotation therewith and beingcoaxial to the yoke, said hub having a machinable outer surface andbeing made of a non-ferromagnetic, non-corrodible material suitable foruse in a clean chamber following machining of the outer surface; anouter peripheral cylindrical surface on said hub dimensioned to passthrough a standardized central opening of a storage disk for receivingand mounting the storage disk for rotation therewith in said cleanchamber, said outer peripheral cylindrical surface radially enclosingsaid soft magnetic annular yoke of said rotor and said stator for asubstantial part of the axial extensions thereof, and at least half ofthe axial longitudinal dimension of the stator winding and of the rotormagnet interacting magnetically therewith being housed within said outerperipheral cylindrical surface of the storage disk mounting portion ofthe hub, and a magnetic shield ring located in the hub and extendingsubstantially from the soft magnetic annular yoke radially inwardly andsubstantially from one axial end of the soft magnetic annularyoke..Iaddend. .Iadd.52. A disk storage drive comprising:a clean chamberfor housing a storage disk; a brushless drive motor having a stator anda winding on the stator, the stator having an axial longitudinaldimension; an external rotor having a rotation axis and coaxiallysurrounding the stator, an inner wall of said rotor being spaced fromsaid stator by a substantially cylindrical air gap, said rotor having apermanent magnet with an axial longitudinal dimension and a softmagnetic annular yoke with an axially extending wall portion, saidpermanent magnet forming the inner wall of said rotor adjacent the airgap; a hub held fast on the rotor for rotation therewith and beingcoaxial to the yoke, said hub having a machinable outer surface andbeing made of a non-corrodible material suitable for use in a cleanchamber; an outer peripheral cylindrical surface on said hub dimensionedto pass through a standarized central opening of a storage disk forreceiving and mounting the storage disk for rotation therewith in saidclean chamber, said outer peripheral cylindrical surface radiallyenclosing said soft magnetic annular yoke of said rotor and said statorfor a substantial part of the axial extensions thereof; and a magneticshield ring located in the hub and extending substantially from oneaxial end of the soft magnetic annular yoke..Iaddend. .Iadd.53. A diskstorage drive as claimed in claim 52, wherein the stator winding and therotor magnet interacting therewith are substantially completely housedwithin the disk mounting portion of the hub..Iaddend. .Iadd.54. A diskstorage drive as claimed in claim 52, wherein the hub is made of lightmetal..Iaddend. .Iadd.55. A disk storage drive as claimed in claim 52,wherein the external circumferential surface of the disk mountingportion of the hub, after assembly of hub and drive motor, is finishedwith respect to centricity with the rotation axis..Iaddend. .Iadd.56. Adisk storage drive as claimed in claim 52, wherein the rotor and the hubare fixed to a rotatable shaft..Iaddend. .Iadd.57. A disk storage driveas claimed in claim 52, wherein the rotor and the hub are fixed to ashaft rotatably supported axially in a bearing system that is at leastpartly housed within the stator of the drive motor..Iaddend. .Iadd.58. Adisk storage drive as claimed in claim 52, wherein a bearing bushreceiving the shaft is formed integrally in the hub or soft magneticannular yoke..Iaddend. .Iadd.59. A disk storage drive as claimed inclaim 58, wherein the bearing system is sealed by means of at least onemagnetic fluid or ferrofluidic seal..Iaddend. .Iadd.60. A disk storagedrive as claimed in claim 59, wherein the magnetic field or ferrofluidicseal is positioned adjacent to but axially spaced from the bearingbush..Iaddend. .Iadd.61. A disk storage drive as claimed in claim 52,wherein the rotor and the hub are rotatably mounted by means of abearing system on a fixed shaft..Iaddend. .Iadd.62. A disk storage driveas claimed in claim 61, wherein leads are provided for the statorwinding that pass through the fixed shaft to the outside of thedrive..Iaddend. .Iadd.63. A disk storage drive as claimed in claim 52,wherein a control magnet is connected to the unit that includes therotor and the hub, and interacts with a stationary magnetic positionsensor..Iaddend. .Iadd.64. A disk storage drive as claimed in claim 63,wherein the control magnet is positioned on that side of the unit thatincludes the rotor and the hub and that is open in the axialdirection..Iaddend. .Iadd.65. A disk storage drive as claimed in claim63, wherein the control magnet is axially aligned with the rotormagnet..Iaddend. .Iadd.66. A disk storage drive as claimed in claim 63,wherein the rotation position sensor is mounted on a printed circuitboard that axially faces the side of the unit that includes the rotorand the hub and that is open in the axial direction..Iaddend. .Iadd.67.A disk storage drive as claimed in claim 52, wherein the ratio of innerand outer diameters of the stator is at least 0.35..Iaddend. .Iadd.68. Adisk storage drive as claimed in claim 67, wherein said ratio is 0.4 to0.7..Iaddend. .Iadd.69. A disk storage drive as claimed in claim 52,wherein the ratio of axial length to external diameter of the statordoes not exceed 1..Iaddend.